1. Field of the Invention
The present invention relates to an ink supply mechanism for supplying ink to an ink jet head, and also, relates to an ink jet recording apparatus.
2. Related Background Art
Of the recording methods for a printer or the like, the ink jet recording method that records on a recording medium, such as a recording paper sheet, by discharging ink from the discharge ports (nozzles) has been widely adopted in recent years, because it performs recording operation at high speed in high density by use of the low-noise non-impact recording method.
In general, an ink jet recording apparatus comprises means for driving a carrier that mounts an ink jet head thereon; conveyance means for conveying a recording paper sheet; and control means for controlling them, among some others. Also, there is the one which uses electromechanical converting elements, such as piezoelectric elements, to exert pressure on ink in order to generate energy for discharging ink from the nozzle portion of an ink jet heat; irradiates electromagnetic waves, such as laser, to generate heat; generates heat for bubbling; or uses electrothermal converting elements each having heat resistive element for heating liquid for bubbling. Among them, the ink jet recording apparatus that adopts the method for discharging ink droplets utilizing thermal energy makes it possible to perform recording in high resolution with the nozzles that can be arranged in high density. Particularly, the ink jet head that uses electrothermal converting elements as energy generating elements can be made smaller with ease, and by the application of the IC technologies and micro-machining techniques, which have made remarkable technical advancement and enhancement of reliability in the field of semiconductor manufacturing in recent years, the ink jet head of the kind can be assembled in high density at lower costs utilizing the advantages of these technologies and techniques sufficiently.
Now, FIG. 5 shows one example of the conventional ink jet recording apparatus that adopts the method of discharging ink droplets utilizing thermal energy, in which the discharge nozzle 101g of a recording head 101 is a fine hole. There is no particular valve mechanism provided for the nozzle. With the interior of the nozzle being kept in negative pressure, the nozzle enables ink to be given meniscus to prevent ink leakage from the nozzle, as well as to prevent the air from entering the nozzle from the atmosphere. Ink is discharged by pushing out ink in the discharge nozzle 101g by means of film-boiling energy of the heater arranged in the vicinity of the discharge nozzle 101g. After discharge, ink is filled again in the nozzle by means of capillary force of the discharge nozzle 101g. This cycle is repeated, and ink is absorbed from the main tank 104 through a tube 106 as required.
In the recording head 101, there are arranged a filter 101c having a fine mesh structure to prevent the discharge nozzle 101g, which is a fine hole, from being clogged by dust particles; the flow path 101f that connects the filter 101c and the discharge nozzle 101g; and the sub-tank 101b for retaining ink in a given amount, which is arranged on the upstream side of the filter 101c, here, ink being supplied thereto by way of the tube 106 from the main tank 104 installed on the main body of the ink jet recording apparatus.
The main tank 104 and the supply base 105 are structured as disclosed in the specification of Japanese Patent Publication 2929804, and the liquid connector 104b on the bottom face of the main tank 104 is detachably installed on two hollow needles 105a and 105b fixed to the supply base 105.
In the supply base 105, there is arranged the ink chamber 105f which is released to the atmosphere by means of an atmospheric port 105g. The hollow needles 105a and 105b are arranged in such a manner that the height of the low end of the hollow needle 105b is made different from that of the hollow needle 105a so as to keep it in ink in the ink chamber 105f. The ink chamber 105f is structured to be communicated with the tube 106 from the bottom portion of the ink chamber 105f. Then, when the lower end of the hollow needle 105b appears on the liquid surface of the ink chamber 105f as the liquid surface of the ink chamber 105f is lowered following the reduction of ink in the ink chamber 105f due to ink consumption, the air enters the interior of the main tank 104 from the lower end of the hollow needle 105b. Thus, ink in the main tank 104 flows out to the ink chamber 105f to raise the liquid surface of ink in the ink chamber 105f to cause the lower end of the hollow needle 105b to be immersed again in ink. With the structure thus formed, ink in the main tank 104 is drawn out gradually.
Also, on the lower part of the main tank 104, the electrode 104e is arranged to be in contact with ink, which is in conduction with the contact point 105j provided for the supply base 105. To the contact point 105j and the hollow needle 105b, the detection circuit 105h, which measures the electric resistance of ink, is connected to detect the presence and absence of ink.
In the sub-tank 101b, the air that permeates the resin material of the tube 106 or the like to enter the sub-tank, and the air dissolved and retained in ink is accumulated as well. Therefore, the accumulated excessive air is sucked out together with ink periodically from the side wall of the sub-tank 101b by means of the exhaust tube 110a and the exhaust pump 110c. Then, the sub-tank is closed by the valve 110b when the exhaust is completed to maintain the ink discharge characteristics.
Also, if overly viscous ink causes the discharge nozzle 101g to be clogged or any excessive bubble that may be generated at the time of discharge ensues in clogging, the recovery of ink discharge characteristics is made by sucking ink intensively from the discharge nozzle 101g by means of the suction pump provided for the suction cap 107a of the recovery unit 107.
Now, however, even if a step is taken to deal with any unexpected movement of ink (such as ink being returned from the head side to the ink chamber 105f) with the provision of a mechanism, which is additionally provided for the ink supply mechanism of the conventional structure exemplified as described above, to close the tube 106 on the midway when operation is at rest, there is still a possibility that ink flows out externally from the atmospheric communication port 105g if the apparatus shown in FIG. 5 is inclined to make its right side higher, for example, due to the occurrence of unusual situation under which the apparatus shown in FIG. 5 moves to change its installation site.
Further, when the ink liquid surface of the ink chamber 105f is caused to part from the end portion of the hollow needle 105b, the leading end of the hollow needle 105b is released to the atmosphere. In this state, the air is induced from the hollow needle 105b into the main tank 104, and ink in the main ink tank 104 flows out to the ink chamber 105f along with the induction of the air. Thus, unless the leading end portion of the hollow needle 105b is clogged by ink, ink in the main tank 104 flows out continuously, and in the worst case, there may occur the event that all ink in the main tank 104 flows out into the ink chamber 105f. The ink chamber 105f is not capable enough to receive all ink in the main tank 104. As a result, ink that flows out from the ink chamber 105f is allowed to flow out externally from the atmospheric communication port 105g eventually. In addition, if the volume of the ink chamber 105f is made large enough to receive all ink in the main tank 104, the structure of the apparatus becomes extremely large, which is not practicable.
Meanwhile, it is an important technique to detect ink remainders in an ink jet recording apparatus in order to protect the head or avoid wasting an object to print on eventually. For example, the structure shown in FIG. 5, in which electrodes are buried in the main tank for purpose of detecting ink remainders, needs the provision of electrodes and more parts at the connecting point therebetween, thus resulting in the increased costs of the apparatus and the main tank inevitably.
Here, for example, the hollow needles 105a and 105b are connected to the detection circuit to form a structure whereby to detect the resistance of ink residing between the two hollow needles in the main tank 104. With this structure, however, the resistance of ink is detected as far as ink exists in the ink chamber 105f even when there is no ink in the main tank 104, and the result of detection may sometimes indicate the presence of ink in the main tank 104, because the hollow needles 105a and 105b are in contact through ink in the ink chamber 105f. Also, even when the main tank 104 is removed, the detection is effectuated to indicate the presence of ink if ink remains in the ink chamber 105f. As a result, irrespective of the presence or absence of the main tank 104, detection indicates that ink is in the normal status, leading to a drawback that the installation status of main tank is not detectable.
With a view to solving the problems discussed above, the present invention is designed to aim at the provision of the ink supply mechanism capable of maintaining the ink supply status stably without being affected by the status (conditions in movement and installation site) of the ink jet recording apparatus that uses such mechanism, as well as the provision of an ink jet recording apparatus.
It is another object of the invention to provide an ink supply mechanism structured to make it difficult for ink in the main tank to leak from the atmospheric communication port, and an ink jet recording apparatus as well.
It is still another object of the invention to provide an ink supply mechanism capable of detecting the presence and absence of ink in the main tank, as well as detecting with ease the state of the main tank being mounted or unmounted, and also to provide an ink jet recording apparatus.
In order to achieve the objects described above, the ink supply mechanism of the present invention for an ink supply device that supplies ink from an ink tank to a recording head comprises an ink tank freely attachable and detachable, which retains ink therein with two connectors provided for the bottom thereof for enabling the inside thereof to be communicated with the outside. For this ink supply mechanism, a first hollow needle, which is communicated with the ink supply path for supplying ink to the recording head, is inserted into one of the connectors for communication, and a second hollow needle, which is communicated with the bottom of the atmospheric communication chamber communicated with the atmosphere through an atmospheric communication port, is inserted into the other one of the connectors for communication in order to form one flow path airtightly closed to the atmosphere from the atmospheric communication port to the ink supply path through the ink tank.
The ink supply device structured as described above enables the first hollow needle connected with the ink supply path and the second hollow needle communicated with the bottom end of the atmospheric communication chamber communicated with the atmosphere through the atmospheric communication port to be inserted into each of the connectors of the ink tank for communication, thus forming one flow path airtightly closed to the atmosphere from the atmospheric communication port to the ink supply path through the ink tank. In other words, with the formation of one airtightly closed flow path from the atmospheric communication port to the ink supply path, it becomes possible to eliminate the flow-in of the air on the midway of the flow path, and the ink leakage as well, and also, to block the movement of ink in the flow path.
Also, for the ink supply device of the present invention, the first hollow needle and the second hollow needle are formed by conductive material, and a circuit may be provided to measure the value of electric resistance between the first and second hollow needles. In this case, the ink that resides between the two hollow needles is only ink in the ink tank. As a result, there is no possibility that the resistance of any ink residing outside the ink tank is detected unexpectedly.
Further, the atmospheric communication chamber is a space expanded from the lower end of the second hollow needle upward, and the atmospheric communication port provided for the atmospheric communication chamber may be arranged at a position higher than the opening of the second hollow needle on the insertion side thereof into the connector for communication, and part of the path between the atmospheric communication port and the second hollow needle may be positioned to be higher than the opening of the second hollow needle on the insertion side thereof into the connector for communication. In this case, it becomes possible to prevent ink leakage from the atmospheric communication port even if the ink tank is mounted erroneously without the installation of the recording head, for example. Also, with the structure of the atmospheric communication chamber as a space expanding from the lower end of the second hollow needle upward, it becomes possible to enable ink in the atmospheric communication chamber to return to the main tank reliably even when the environmental condition is restored while ink has leaked into the atmospheric communication chamber due to the environmental changes or the like or even if ink is supplied while the recording is performed in a state of ink residing in the atmospheric communication chamber. In this way, there is no possibility that ink is consumed wastefully.
Also, the volume of the atmospheric communication chamber may be set to satisfy Va greater than Vtxc3x97(T2xe2x88x92T1)/T2 where T1 is the lower limit temperature of use environmental temperature; T2 is the upper limit temperature of use environmental temperature; Va is the volume of the atmospheric communication chamber; and Vt is the volume of the ink tank. In this case, even if the temperature of the use environment is caused to change to push out ink due to the resultant changes of inner pressure of the ink tank, the atmospheric communication chamber has the volume good enough to function as a buffer chamber for the ink that has been pushed out, thus retaining ink thus pushed out to prevent ink leakage from the atmospheric communication port.
The ink supply mechanism of the present invention comprises an ink supply path for supplying ink to a recording head connected with an ink tank capable of being attached to and detached from a recording apparatus; and an atmospheric communication path connected with the ink tank to condition the ink tank to be communicated with the atmosphere. For this supply mechanism, the ink supply path and the atmospheric communication path are made communicative as one path through the ink tank only in the state of being connected with the ink tank, and the ink supply path and the atmospheric communication path are cut off when the ink tank is not mounted.
With the ink supply mechanism of the present invention thus structured, it becomes possible to make the ink supply path and the atmospheric communication path one communicative path through the ink tank. In other words, the passage between the atmospheric communication port and the ink supply path is made one flow path which is airtightly closed to eliminate the flow-in of the air from the midway of the flow path, and the ink leakage as well, while blocking the movement of ink in the flow path. Also, when ink is not mounted, the ink supply path and the atmospheric communication path is cut off to condition them to be independent from each other. For example, therefore, if only the electrical conduction across the ink supply path and the atmospheric communication path is examined, it becomes possible to determine whether or not the ink tank is mounted.
The ink jet recording apparatus of the present invention is provided with conveying means for conveying a recording medium to perform recording by discharging ink from a recording head to the recording medium, which comprises an ink supply mechanism of the present invention.
The ink jet recording apparatus of the invention structured as described above is provided with the ink supply device of the invention to make it possible to prevent ink leakage from the atmospheric communication port. Also, the presence and absence of ink in the ink tank can be grasped exactly. Whether or not the ink tank is mounted can be grasped, too.